Frequently Asked Questions

The z test to compare two proportions.

The chi-square test is equivalent to the z test. The two make the same assumptions and report the same P value. The only difference is that the chi-square test computes a value for chi-square, which Prism reports (see page 55 of Fleiss, reference below). The z test, in contrast, computes a value for the z ratio. Prism and InStat do not report this ratio, but it would equal the square root of chi-square.

When comparing two proportions, the chi-square test can be done two ways: With and without the Yates' correction. Likewise, the z test, can be done with and without the Yates' correction.